WO2025208043A1 - Precision pan axis for a stereo camera bar tracking system - Google Patents

Abstract

A precision motorized stereo camera bar is integrated with a rotational axis a to increase the useful field of view of camera tracking systems for continuous scanning without realignment. Each camera tracking system has at least one motorized axis of rotation to allow for measurement over large and complex volumes.

Description

PRECISION PAN AXIS FOR A STEREO CAMERA BAR TRACKING SYSTEM

RELATED APPLICATIONS

[0001] The present application claims priority to U.S. Provisional Application No. 63/571,747, filed on March 29, 2024, the entire contents of which is incorporated herein by reference.

BACKGROUND

[0002] The present disclosure relates to an improved three-dimensional (3D) object tracking system including a camera bar, and more specifically relates to a tracking system which uses a pan axis stereo camera bar to increase the trackable volume of space.

[0003] Known stereo camera bars have a fixed field of view that need to be realigned whenever it is moved. These types of stereo camera bars are commonly used for precision 6-degrees of freedom (DoF) tracking of hand-held or machine/robot mounted measurement devices, and other objects and artifacts within a scanned environment. Some stereo camera bars track the position of the measurement devices using the principle of triangulation to determine 3D coordinates of points on surfaces of a target object within the environment, by determining the position of the measurement device while measurements are made. In such systems, it is desired to accurately track the position of the measurement device, since small errors in triangulation computations typically compound as the device is moved.

[0004] Accordingly, while existing tracking systems are suitable for their intended purposes there remains a need for improvement, particularly in providing a stereo camera bar system having the features described herein.

BRIEF DESCRIPTION

[0005] According to one aspect of the present disclosure, a method for tracking a measurement device is provided. The method includes moving the measurement device into an active measurement volume of a stereo camera system having at least one rotational degree of freedom, the stereo camera system tracking the measurement device within the active measurement volume based on visible targets of the measurement device. The method also includes determining whether a kinematic of the measurement device exceeds a threshold value, and rotating the stereo camera system about the at least one rotational degree of freedom to center the active measurement volume on the visible targets of the measurement device in response to determining the kinematic of the measurement device exceeds the threshold value. The method further includes capturing a first measurement of a target object in the active measurement volume using the measurement device, and determining a first pose of the measurement device when the measurement device captures the first measurement using the stereo camera system, where the first pose is associated with the first measurement. The method further includes capturing a second measurement of the target object in the active measurement volume using the measurement device and determining a second pose of the measurement device when the measurement device captures the second measurement using the stereo camera system, where the second pose is associated with the second measurement.

[0006] According to another aspect of the present disclosure, a method for tracking a measurement device is provided. The method includes moving the measurement device into an active measurement volume of a stereo camera system having at least one rotational degree of freedom, the stereo camera system tracking the measurement device within the active measurement volume based on visible targets of the measurement device. The method also includes determining a distance from the measurement device to an edge of the active measurement volume and rotating the stereo camera system about the at least one rotational degree of freedom to center the active measurement volume on the visible targets of the measurement device in response to the distance exceeding a threshold value. The method further includes capturing a first measurement of a target object in the active measurement volume using the measurement device, determining a first pose of the measurement device when the measurement device captures the first measurement using the stereo camera system, and transforming the first pose of the measurement device based on the rotation of the stereo camera system when determining the first pose of the measurement device, where the transformed first pose is associated with the first measurement. The method further includes capturing a second measurement of the target object in the active measurement volume using the measurement device, determining a second pose of the measurement device when the measurement device captures the second measurement using the stereo camera system, and transforming the second pose of the measurement device based on the rotation of the stereo camera system when determining the second pose of the measurement device, where the transformed second pose is associated with the second measurement.

[0007] According to a further aspect of the present disclosure, a method for tracking a measurement device is provided. The method includes moving the measurement device into an active measurement volume of a stereo camera system having at an axis of rotation, the stereo camera system tracking the measurement device within the active measurement volume based on visible targets of the measurement device. The method also includes determining a distance from the measurement device to an edge of the active measurement volume, determining a velocity of the measurement device towards the edge of the active measurement volume, and rotating the stereo camera system about the axis of rotation to center the active measurement volume on the visible targets of the measurement device in response to the distance exceeding a threshold value. The method further includes capturing a first measurement of a target object in the active measurement volume using the measurement device, determining a first pose of the measurement device when the measurement device captures the first measurement using the stereo camera system, and transforming the first pose of the measurement device based on the rotation of the stereo camera system when determining the first pose of the measurement device, where the transformed first pose is associated with the first measurement. The method further includes capturing a second measurement of the target object in the active measurement volume using the measurement device, determining a second pose of the measurement device when the measurement device captures the second measurement using the stereo camera system, and transforming the second pose of the measurement device based on the rotation of the stereo camera system when determining the second pose of the measurement device, where the transformed second pose is associated with the second measurement. The threshold value increases and decreases based on the velocity and the acceleration of the measurement device.

[0008] These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The foregoing and other features and advantages of the disclosure are apparent from the following detailed description taken in conjunction with the accompanying drawings, of which:

[0010] FIG. 1 is a perspective view of a stereo camera bar with one axis of rotation according to an embodiment of the present disclosure;

[0011] FIG. 2 is a perspective view of a tracking camera with two axes of rotation according to an embodiment of the present disclosure;

[0012] FIG. 3A is a perspective view of a handheld measurement device according to an embodiment of the present disclosure;

[0013] FIG. 3B is a perspective view of a second configuration of a hand-held measurement device according to an embodiment of the present disclosure.

[0014] FIG. 4 A is a top down view of a measurement volume using the stereo camera bar of FIG. 1 in a fixed position according to an embodiment of the present disclosure; and

[0015] FIG. 4B is a top down view of a measurement volume using the stereo camera bar of FIG. 1 in rotation according to an embodiment of the present disclosure.

[0016] FIG. 5 depicts an exemplary process for using a stereo camera bar in accordance with various embodiments. [0017] The detailed description explains embodiments of the disclosure, together with advantages and features, by way of example with reference to the drawings. While definite examples of various implementations are described herein for purposes of clarity, it will be appreciated that other modifications and configurations are readily contemplated, and the examples herein throughout are not to be limited thereto.

DETAILED DESCRIPTION

[0018] Improvements described herein below include systems and methods that improve the accuracy of large volume measurements. Another improvement is in providing ways to accurately take large volume measurements without having to reposition a measuring device.

[0019] Typical stereo camera bars use two fixed cameras which are able to triangulate the position of an object, such as a measurement device for example, when the object is positioned in an area where the two camera’s field of view overlap. However, current stereo camera bars have a limited measurement volume, which is defined by a balance of desired tracking accuracy, camera sensor resolution, camera lens field of view, and camera spacing, among other factors. Practical limitations in size and cost of the tracking cameras used in the stereo camera bar system also limits the measurement volume of such systems.

[0020] In some embodiments, the volume of area that is tracked, i.e., the overlapping region of the tracking cameras’ fields of view, is increased by adjusting the position of the cameras to be farther apart or by using a wide angle camera lens in the cameras. However, using a wide angle lens will reduce the image resolution and accuracy of the cameras, and positioning the cameras farther apart will increase their distance from the object being tracked, thereby decreasing resolution. When the object being tracked is located far away from the cameras, the object appears smaller in the acquired images and errors in triangulating the position of the object thus increase.

[0021] Conversely, using a camera with a smaller field of view (i.e., with a high focal length) will improve the resolution of the image and the accuracy of the position triangulation. However, the drawback to this arrangement is that the camera’s field of view is smaller and therefore tracks the desired object over a concomitantly decreasing volume of space.

[0022] The measurement of larger objects (e.g., an automobile) involves a larger measurement volume or field of view than is available with “standard” stereo camera bar products. In these situations, the operator will either provide additional camera bars about the object to cover the desired measurement volume, or the operator will interrupt the measurement process to reposition and realign the camera bar. The additional user workflow of repositioning and computing the alignment between these different positions of the camera bar adds time and complexity to completing the measurements of a large volume, while reducing accuracy of the measurement job throughout.

[0023] Referring now to FIG. 1, a stereo camera bar 10 is shown according to various embodiments of the present disclosure. The stereo camera bar 10 includes a first camera 11A and a second camera 11B mounted on opposite ends of a bar 13, although the number of cameras is greater than two in certain contemplated instances. In the illustrated embodiment, the bar 13 is substantially rigid and holds the cameras 11 A, 11B at a fixed equidistant distance from each other (i.e., a base length). Both cameras 11 A, 1 IB have a static lens with a fixed focal length, or in some embodiments, a zoom lens having an adjustable focal length that enables magnification of a visible target. In some embodiments, the lenses are switched out, alternated and replaced depending on the workflow and volume of measurement. The bar 13 is rotatably mounted on a motor 17 and rotates about a Z-axis 16 that is orthogonal to the length of the bar 13 along an X-axis 19. The motor 17 is mounted on a tripod 15 or another stand, for example a post. In an embodiment the bar 13 is rotatably mounted on the tripod 15 and is operatively connected to the motor 17, directly or via a drive train, such that the motor 17 rotates the bar 13 about the Z-axis 16. This axis of rotation is referred to herein as an “azimuth” or “pan” axis. [0024] In various embodiments, the motor 17 is a servo motor, actuator or other precision spindle which fluidly and continuously rotates the bar 13 and cameras 11 A, 11B. In certain instances, the motor 17 is the same as or similar to motors used with articulated arm coordinate measurement machines (AACMM) known in the art, examples of which are described in commonly-owned United States Patent No. 11,874,101 entitled “Modular Servo Cartridges for Precision Metrology,” the entirety of which is hereby incorporated by reference. It should be appreciated that the rotating of the cameras 11 A, 1 IB about the Z-axis 16 allows the field of view for the cameras to be adjusted without having to perform any calibration or compensation methods. Thus, the effective field of view for the rotating stereo camera bar 10 is not a pentagonal prism shape that is typical of a fixed camera bar system, but is instead a torus shape, an example of which is depicted in FIG. 4B.

[0025] In an embodiment, a rotary encoder 18 is provided that measures the rotational position of the bar 13 about the Z-axis 16. Examples of suitable rotary encoders are described in commonly owned United States Patent No. 9,410,787 entitled “Portable Coordinate Measurement Machine Having a Bearing Assembly with an Optical Encoder,” the entirety of which is hereby incorporated by reference. In certain embodiments, the rotary encoder 18 measures the rotational position to an accuracy of 200 micro-degrees or less. This rotational position data from the rotary encoder 18 is stored with each pair of acquired images (e.g. each frame) from the tracking cameras 11 A, 11B. In this way, a 3D measurement of an object in the cameras’ fields of view when the bar 13 is at a first rotational position is transformed into a common frame of reference, along with such measurements performed at additional rotational positions.

[0026] In various embodiments, the motor 17 is hidden from view and is connected to the bar 13 via a drive train or other means for translating motion. For example, the motor 17 is mounted at the base of a stand or the tripod 15 that supports the bar 13 in some instances. Furthermore, while the stereo camera bar 10 is described with one motor and one degree of freedom of motion about an axis, in other embodiments, the stereo camera bar 10 includes any combination of one or more motors and one or more axes of rotation. For example, the stereo camera bar 10 sometimes includes a single motor that operatively connects to, and is switched between, multiple drive trains, each of which rotating the bar 13 about a respective axis. In some configurations, multiple motors are used to rotate the bar 13 about a single axis in order to precisely adjust the speed or precision of rotation.

[0027] In an embodiment, the stereo camera bar 10 and the motor 17 are a factory installed component such that the motor 17 is integral to the camera bar itself. In other embodiments, the motor 17 is an optional accessory that is added to preexisting fixed camera bars to provide rotational capabilities. In an embodiment where the motor 17 is added to preexisting camera bars, a kinematic mounting system is used to reduce, minimize or eliminate the performing of calibration steps on the cameras due to installation/removal of the motor. For example, in some embodiments, a kinematic mount is similar to that described in commonly owned United States Patent No. 10,663,274 entitled “Articulated Arm Coordinate Measuring Machine,” the entirety of which is hereby incorporated by reference. The use of a kinematic mount significantly reduces the necessity and frequency of performing camera compensation methods to calibrate cameras 11 A, 1 IB of the stereo camera bar 10.

[0028] In some embodiments, the cameras 11 A, 11B are independently rotatable cameras mounted on the bar 13. For example, in some embodiments, the cameras 11 A, 1 IB are rotatable about a first axis and a second axis perpendicular to the first axis in addition to the rotation of the bar 13 about the Z-axis 16. In this way, the stereo camera bar 10 provides more precise and targeted adjustments to the active measurement volume of the stereo camera bar 10.

[0029] FIG. 2 illustrates, a stereo camera bar 10 now having two axes 16, 19 of rotation. In this embodiment, the cameras 11 A, 1 IB are mounted to a bar 13 having an additional second motor 22. The second motor 22 is configured to rotate the bar 13, and thus the cameras 11 A, 1 IB about an X-axis 19 that runs along the length of the bar 13, and in various embodiments through a central axis along the length of the bar 13. In an embodiment, the X-axis 19 extends through the perspective centers of the lenses of the cameras 11 A, 1 IB. In this embodiment, the X-axis 19 is orthogonal or perpendicular to the Z-axis 16. It should be appreciated that providing bi-directional rotation about both the X-axis 19 and Z-axis 16 further increases the effective field of view of the stereo camera bar 10. Thus, in an embodiment, the effective field of view for the stereo camera bar 10 is a toroidal or a spherical shape.

[0030] Referring now to FIG. 3A, a measurement device 30 is shown that includes a handheld scanner 31 having a collection of visible targets 33 attached thereto in such manner as to form a cage or the like around the handheld scanner 31, according to various embodiments. In some embodiments, the visible target 33 are affixed directly on the handheld scanner 31, for example adhesive retro-reflectors. In some embodiments, the cage protects the handheld scanner 31 from damage due to droppage or the like. In additional embodiments, the cage is in any of a variety of configurations other than the exact configuration shown in FIG. 3 A. Another exemplary configuration of a cage is shown in FIG. 3B. In these and various contemplated embodiments, the cage allows access for an arm of a human operator (as shown) or a support structure (not shown) to hold the handheld scanner 31

[0031] Inn various embodiments, the visible targets 33 are one or more of adhesive retro-reflectors, reflective dots, other useful reflectors and/or active light emitting diodes (LEDs). Adhesive reflectors or retroreflective targets are illuminated by a light source (not shown) associated with the stereo camera bar 10 to enable identification and tracking of the position of the handheld scanner 31 in various instances. In some instances, reflections of light from each reflector returns a code when illuminated that is used by a processor or the like to, for example, identify the particular reflector, which is then of determinable, i.e., known or calculable, orientation with respect to the pose of the handheld scanner 31. The orientation is “known,” in various embodiments, by referencing an electronically-stored look-up table or database that holds digital records of (i) the position of the identified reflectors (as by their geometric shape or the like) and/or (2) codes reflected thereby when illuminated. In various embodiments, the values described for (i) and (ii) above are stored along with one or more corresponding values indicating the orientation of the handheld scanner 31 having such reflectors and/or returning such codes. The orientation is “calculable” where the processor uses programmed geometric algorithms or the like to determine an orientation of reflectors by their determined geometric shapes as identified from image data collected by the cameras.

[0032] In embodiments using active LEDs in place of or in conjunction with reflectors, the LEDs are continuously illuminated in some embodiments, while in others the various LEDs are flashed in a coded pattern or at specific intervals to help identify and center the corresponding LED in each image of the camera. In some embodiments, the collection of visible targets 33 are coupled to a frame 35 forming the previously- described cage, which is removably attached to the handheld scanner 31. In other embodiments, the visible targets 33 are directly affixed or adhered to the handheld scanner 31 with connector elements or the like.

[0033] In an embodiment, the measurement device 30 is directly connected to communicate with an external computer, such as a workstation computer or networked computer (not shown) to perform some or all of the data processing, storage and calculations described herein. Alternatively, the measurement device 30 is coupled to communicate with a wearable unit that includes a computing unit and an independent power source (such as a battery) that is ported by an operator of the measurement device 30.

[0034] In an embodiment, the measurement device 30 is a structured light scanner that measures 3D coordinates on surfaces of the target object being measured using laser light. In other embodiments the handheld scanner 31 is, without limitation, a 2D laser scanner, a 3D laser scanner, a hard probe, an enclosure housing a laser line probe, a laser projector, a laser tracker, a portable coordinate measurement machine, or a combination thereof, examples of which are described in detail in commonly-owned United States Patent No. 11,908,162 entitled “Line Scanner Having Target-Tracking and Geometry-Tracking Modes, the entirety of which is hereby incorporated by reference. [0035] FIG. 4A illustrates the stereo camera bar 10 being used in a first mode of operation in which it is placed in a fixed position to track the measurement device 30. The first camera 11 A and the second camera 1 IB of the stereo camera bar 10 each have respective fields of view 41 A, 41B. The fields of view 41 A, 41B together represent the trackable area of the respective camera 11 A, 11B, the intersection of which is the active measurement volume 43 of the stereo camera bar 10. When a target object 45 being measured fits within the measurement volume 43, the stereo camera bar 10 is typically used in this first mode of operation. The measurement volume 43 of the stereo camera bar 10 is generally a prism and in some embodiments is a pentagonal prism. The six degree of freedom (6-DOF) pose of the measurement device 30 is determined when in the measurement volume 43 based on images acquired of the visible targets 33 thereon. In this way, the measurements of the location of the target object 45 by the stereo camera bar 10 are used by the handheld scanner 31, or connected processing system, and transformed into a global coordinate frame of reference for all the measurements by the measuring device 30 within an environment.

[0036] The stereo camera bar 10 captures images of the visible targets 33 of a measurement device 30 (such as the handheld scanner 31) and uses those captured images to track the pose (position and orientation) of measurement device 30 as it is moved from position to position by an operator. In an embodiment, electrical signals from the stereo camera bar 10 are sent over a wired or wireless communication channel to a computing system (processor) that determines the 3D coordinates of the measurement device 30. To perform this calculation, the computing system needs to determine the relative pose (position and orientation) of the stereo camera bar 10. In an embodiment, the relative pose of the stereo camera bar 10 is determined by performing a compensation procedure in the field. An exemplary compensation procedure involves capturing a pattern on an artifact, such as a standardized dot plate with known sizes and positions of reflective or LED target elements, which is placed in the cameras’ overlapping fields of view. In some embodiments, such an artifact is moved to a plurality of positions and orientations, and the stereo camera bar 10 is used to capture images in each case. Optimization methods such as, but not limited to bundle adjustment are then used to determine the relative pose of the stereo camera bar 10. Such use of bundle adjustments are described in commonly-owned United States Patent No. 10,455,216 entitled “Three-Dimensional Imager,” the entirety of which is hereby incorporated by reference.

[0037] FIG. 4B illustrates stereo camera bar 10 in a second mode of operation that allows for rotation of the bar 13 around two axes 16, 19, thereby enabling cameras 11 A, 1 IB to track a measurement device 30 over a wider field of view. Similar to FIG. 4A, the cameras 11 A, 1 IB of the stereo camera bar 20 having respective fields of view 41A, 41B has an active measurement volume 43 based on their overlapping fields of view. The stereo camera bar 10 rotates (clockwise and/or counter-clockwise) to adjust the orientation of the cameras 11 A, 11B and to change the position of the active measurement volume 43, thus allowing the stereo camera bar 10 to measure larger and more complex volumes than would otherwise be possible for a fixed stereo camera bar. The stereo camera bar 10 rotates 360 degrees around each axis of rotation in various embodiments, thereby defining a potential measurement volume 47 that defines all areas that are able to be covered by the stereo camera bar 10 through available rotations. In various instances, the potential measurement volume 47 is a torus that excludes a circular area around the camera bar system itself.

[0038] In an exemplary embodiment the stereo camera bar 10 and measurement device 30 are used to take measurements of a larger object 46, such as an automobile or the like. When the object 46 is larger than the active measurement volume 43, the stereo camera bar 10 rotates clockwise or counter clockwise to change the position of the active measurement volume 43 such that it includes each section of the object 46 as the measurement device 30 is moved by an operator or mobile apparatus.

[0039] For usage within the active measurement volume 43 of the stereo camera bar 10, the axis of rotation remains inactive (as illustrated in FIG. 4A). In such embodiments, the stereo camera bar 10 reports its static position. However, once the operator moves close to the edges of the active measurement volume 43 (for example, when measuring large or complex objects) the motor 17 activates to rotate the stereo camera bar 10 such that the measurement device 30 and the visible targets 33 thereon are returned to the center of the active measurement volume 43. In an embodiment, the rotation of the stereo camera bar 10 is initiated when the operator moves the measurement device 30 within a predetermined distance of the edge of the active measurement volume 43. In some embodiments, this process is similar to being a type of “servo loop” with a large hysteresis or “dead zone” where no action is taken. Adjusting the parameters of when the stereo camera bar 10 rotates to center on the measurement device 30 and the visible targets 33 will impact the resolution, accuracy, and efficiency of the measurements made by the stereo camera bar 10.

[0040] Mathematically, in determining the position of the measurement device 30, the axis of rotation is applied as a secondary transformation or frame of reference applied to the 6-DoF pose calculated in the fixed reference frame of the stereo camera bar 10. The net (i.e., transformed) pose of the tracked artifact is then the combination of the pose in a Model Confidence Set (MCS) calculated by the stereo camera bar 10 and transformed by the variable reference frame defined by its rotational axis or axes. An MCS is a set of models, e.g., a set of poses of the tracked artifact, which contains the best model within a given level of confidence. In other words, the MCS is analogous to a confidence interval for a given parameter.

[0041] FIG. 5 depicts an exemplary process for using a stereo camera bar in accordance with various embodiments. A method 500 is provided for using a stereo camera bar 10 to track a measurement device 30 imaging a target object 45 begins by setting up the stereo camera bar in operation 501. In some embodiments, setting up the stereo camera bar 10 includes calibrating the cameras 11 A, 11B and establishing an active measurement volume 43, and a potential measurement volume 47 of the stereo camera bar 10, where the target object 45 is within the potential measurement volume 47. A measurement device 30 is then moved into the active measurement volume 43 in operation 503 of the process 500. The stereo camera bar 10 will detect visible targets 33 on the measurement device 30 and will begin tracking the pose of the measurement device 30 based thereon. [0042] The measurement device 30 then images or otherwise measures a portion of the target object 45 in operation 505. At operation 507, the stereo camera bar 10 determines whether the measurement device 30 is “near” an edge of the active measurement volume 43. In some embodiments, “near” the edge of the active measurement volume 43 is a predetermined threshold, e.g., a set distance from the edge of the active measurement volume 43, such as being within a percentage distance (e.g. 10%) to an edge of the field of view. In some embodiments, the determination is instead based on movement of the measurement device 30, e.g., a velocity of the measurement device 30 towards the edge of the active measurement volume 43. In some embodiments, the determination is based on increases or decreases in the movement of the measurement device 30, e.g., an acceleration of the measurement device 30. In additional embodiments, the determination is made based on one or more of the foregoing measures, or a combination thereof. The methods of determining an approach to an edge of the measurement 43 are, however, not limited to these described kinematics. In some embodiments, at least one of these kinematics (i.e., the position, velocity, and acceleration of the measurement device 30), is compared against a predetermined threshold value to determine whether the stereo camera bar 10 needs to rotate to maintain the measurement device 30 within the active measurement volume 43. For example, in some embodiments, the stereo camera bar 10 will determine based on the velocity and position of the measurement device 30 within the active measurement volume 43 that the measurement device 30 will imminently exit the active measurement volume. The stereo camera bar 10 will then rotate to maintain the measurement device 30 within the active measurement volume 43.

[0043] In some embodiments, a variable threshold value is used to determine whether the stereo camera bar 10 rotates to maintain the measurement device 30 within the active measurement volume 43 the based on a combination of the positon, velocity, and acceleration of the measurement device 30. For example, a distance tolerance to the edge of the active measurement volume 43 will decrease when the velocity of the measurement device 30 towards the edge of the active measurement volume 43 increases, and the distance tolerance to the edge of the active measurement volume 43 will increase when the velocity of the measurement device 30 towards the edge of the active measurement volume 43 decreases. In this manner, the threshold value at which the stereo camera bar 10 rotates to maintain the measurement device 30 within the active measurement volume 43 will vary depending on the combination of the position, velocity, and acceleration of the measurement device 30.

[0044] If the measurement device 30 is determined to be near the edge of the active measurement volume 43, the stereo camera bar 10 rotates to center the active measurement volume 43 on the measurement device 30 (operation 509). In some embodiments, the stereo camera bar 10 will continuously rotate to match the movement of the measurement device 30 in real time. In some embodiments, the stereo camera bar 10 will rotate a set amount that is necessary to center the active measurement volume 43 on the measurement device 30. In some embodiments, the measurement device 30 is continuously kept in the center of the active measurement volume 43 by small rotational adjustments by the stereo camera bar 10 tracking the movement of the measurement device 30.

[0045] Once the stereo camera bar 10 rotates such that the measurement device 30 in the active measurement volume 43, the stereo camera bar 10 records the pose of the measurement device 30 including a transformation of the variable reference frame defined by the rotation of the stereo camera bar 10 about its axes or axis and associates the pose of the measurement device 30 with the image or measurement taken in operation 511. If the measurement device 30 is determined not to be near the edge of the active measurement volume 43, then operation 509 is bypassed and the stereo camera bar 10 records the pose of the measurement device 30 (operation 511).

[0046] At operation 513, if the target object 45 is not finished being imaged, then operations 505, 507, 509, and 511 are repeated until the object 45 is finished being imaged, at which point target object imaging ends in operation 515. In some embodiments, operation 515 includes a shutdown procedure, whereby the images and poses are stored in a database, the stereo camera bar 10 and the measurement device 30 are powered down, and the stereo camera bar 10 is disassembled. [0047] In additional embodiments, the handheld scanner 31 is removable from the frame 35, which is adapted to hold a wide variety of payloads including probes, kinematic mounting systems, probe interface electronics, grip/buttons, articulated arm coordinate measuring machine (AACMM) components and the like. In various embodiments, the frame 35 also includes additional electronics for image processing and data synchronization, such as those that are typically found in an AACMM, such as the FAROARM manufactured by FARO Technologies, Inc. In some embodiments, such a system is provided without a payload to operators for tracking robotic arms or other such systems with high accuracy and are adaptable for use with the base of an AACMM or the like to allow rapid device movements within a larger volume.

[0048] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present disclosure. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, element components, and/or groups thereof.

[0049] While the disclosure has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the disclosure is not limited to such disclosed embodiments. Rather, it can be modified to incorporate any number of variations, alterations, substitutions, or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the disclosure. Additionally, while various embodiments have been described, it is to be understood that aspects of the disclosure may include only some of the described embodiments. Accordingly, the disclosure is not limited by the foregoing description.

Claims

What is claimed is:

1. A method for tracking a measurement device, the method comprising: moving the measurement device within an active measurement volume of a stereo camera system, the stereo camera system having at least one rotational degree of freedom; tracking the measurement device within the active measurement volume by identifying visible targets therein that are associated with the measurement device; capturing a first measurement of an object in the active measurement volume using the measurement device; determining a first pose of the measurement device when the measurement device captured the first measurement, using the stereo camera system; associating the first pose with the first measurement; capturing a second measurement of the target object in the active measurement volume using the measurement device; determining a second pose of the measurement device when the measurement device captured the second measurement, using the stereo camera system; associating the second pose is with the second measurement; transforming the first measurement into a transformed first measurement based on the first pose; transforming the second measurement into a transformed second measurement based on the second pose; and determining a three-dimensional coordinate on the object based on the transformed first measurement and the transformed second measurement.

2. The method of claim 1, wherein the first pose of the measurement device is based on a first measured rotation of the stereo camera system in at least one rotational degree of freedom at a time of the first measurement; and the second pose of the measurement device is based on a second measured rotation of the stereo camera system in at least one rotational degree of freedom at a time of the second measurement.

3. The method of claim 1, wherein determining the first pose further comprises: receiving light from the visible targets by the stereo camera system; and determining an orientation of the visible targets relative to the measurement device during the first measurement based on the light.

4. The method of claim 1, wherein determining the second pose further comprises: receiving light from the visible targets; and determining an orientation of the visible targets relative to the measurement device during the second measurement based on the light.

5. The method of claim 1, further comprising determining whether a kinematic of the measurement device exceeds a threshold value; and rotating the stereo camera system about the at least one rotational degree of freedom to center the active measurement volume on the visible targets of the measurement device when the kinematic of the measurement device exceeds the threshold value.

6. The method of claim 5, wherein the kinematic is at least one of: a position of the measurement device within the active measurement volume; a velocity of the measurement device; and an acceleration of the measurement device.

7. The method of claim 1, wherein the stereo camera system rotates to maintain the measurement device in the center of the active measurement volume based on the kinematic and the threshold value.

8. The method claim 1, wherein the measurement device is at least one of: a hard probe; a laser line scanner; an enclosure housing a laser line probe; a handheld scanner; and a coordinate measurement machine.

9. The method of claim 1, wherein the visible targets are at least one of: reflectors; reflective dots; and active light emitting diode (LED) devices.

10. A method for tracking a measurement device, the method comprising: moving the measurement device into an active measurement volume of a stereo camera system having at least one rotational degree of freedom, the stereo camera system tracking the measurement device within the active measurement volume based on visible targets disposed about the measurement device; determining a kinematic of the measurement device with respect to an edge of the active measurement volume; rotating the stereo camera system about the at least one rotational degree of freedom to center the visible targets of the measurement device within the active measurement volume when the kinematic exceeds a threshold value; capturing a first measurement of an object in the active measurement volume using the measurement device; determining a first pose of the measurement device at a time of the first measurement using the visible targets; transforming the first measurement into a first transformed measurement based on the first pose of the measurement device; capturing a second measurement of the object in the active measurement volume using the measurement device; determining a second pose of the measurement device at a time of the second measurement using the visible targets; transforming the second measurement into a second transformed measurement based on the second pose of the measurement device; and determining a three-dimensional coordinate of a surface of the object based on the first transformed measurement and the second transformed measurement.

11. The method of claim 10, further wherein the kinematic comprises a velocity of the measurement device towards the edge of the active measurement volume.

12. The method of claim 11, further comprising rotating the stereo camera system about the at least one rotational degree of freedom to center the active measurement volume on the visible targets of the measurement device in response to the velocity exceeding the threshold value.

13. The method of claim 10, wherein the kinematic comprises an acceleration of the measurement device towards the edge of the active measurement volume.

14. The method of claim 13, further comprising rotating the stereo camera system about the at least one rotational degree of freedom to center the active measurement volume on the visible targets of the measurement device in response to the acceleration exceeding the threshold value.

15. The method of claim 10, wherein the kinematic comprises a distance of the measurement device from the edge of the active measurement volume.

16. The method of claim 15, further comprising rotating the stereo camera system about the at least one rotational degree of freedom to center the active measurement volume on the visible targets of the measurement device in response to the distance exceeding the threshold value.

17. A method for tracking a measurement device, the method comprising: moving the measurement device into an active measurement volume of a stereo camera system, the stereo camera system having at least one axis of rotation for tracking the measurement device within the active measurement volume based on visible targets disposed on the measurement device; determining a kinematic of the measurement device with respect to an edge of the active measurement volume; rotating the stereo camera system about the at least one axis of rotation to center the active measurement volume on the visible targets of the measurement device in response to the kinematic exceeding a stored value; capturing a first measurement of an object in the active measurement volume using the measurement device; determining a first pose that the measurement device was in at a time of the first measurement; transforming the first measurement into a transformed first measurement based on the first pose of the measurement device; capturing a second measurement of the object in the active measurement volume using the measurement device; determining a second pose that the measurement device was in at a time of the second measurement using the stereo camera system; transforming the second measurement into a transformed second measurement based on the second pose of the measurement device; wherein the threshold value increases and decreases based on the kinematic.

18. The method of claim 17, wherein the stereo camera system comprises a first camera and a second camera separated by a bar.

19. The method of claim 18, wherein the at least one axis of rotation includes a first axis of rotation that is perpendicular to a second axis of rotation.

20. The method of claim 18, wherein the first camera and the second camera are independently rotatable about both the first axis of rotation and the second axis of rotation.